The tendencies of iron or steel surfaces to corrode is well known. Zinc is one of the most widely used metallic coatings applied to steel surfaces to protect them from corrosion. Zinc has been electroplated on steel surfaces from various plating baths, preferably from acid plating baths, for providing protection of steel surfaces for various uses.
It is known from U.S. Pat. No. 2,419,231 to Shanz to improve corrosion resistance of the coating by using for the coating an alloy high in zinc and low in nickel. The alloy is co-deposited from the electrotic plating bath onto the steel substrate.
U.S. Pat. No. 4,282,073 to Hirt et al, which is herein incorporated by reference, discloses a process for electroplating steel surfaces in which the present invention can provide an improvement.
U.S. Pat. No. 4,608,091 discloses the use of hydrogen peroxide for use in compositions useful for the selective stripping of protective hard surfaces, coatings and nickel-based brazes from metals. For stripping steel, a composition containing hydrogen peroxide and phosphorous-oxy acid is preferred.
U.S. Pat. No. 4,416,737 to Rustin et al, which is herein incorporated by reference, discloses a process for the electrodeposition of a nickel-zinc alloy on a stell substrate from a nickel salt-boric acid electrolyte containing at least about 40 ppm zinc at temperatures ranging from about 120.degree. to 160.degree. F. The process includes the step of adding hydrogen peroxide to the plating solution to oxidize the iron contaminate and to precipitate it, and then remove the precipitate from the solution. An amount of 0.5 ml of hydrogen peroxide to a liter of Watts nickel bath containing 117 mg/1 iron was proposed.
It has been discovered that in a process for electroplating a steel surface utilizing a zinc sulfate electroplating solution and dilute sulfuric acid rinsing water, the electrochemical corrosion of the stainless steel conductor rolls accounts for approximately 16% of the actual diameter loss of the rolls. This suggests a synergistic effect between electrochemical corrosion and mechanical wear. Applicants hvae found that the corrosion rate increases as the temperature increases (from 55.degree. to 75.degree. C.).
Considering the corrosion aspect, the mechanisms were found to be a cyclic change between electrochemically active and passive states. That is, if there are zinc deposits on the surface of the conductor rolls while they are immersed in the rinsing water, the zinc deposits activate the conductor roll surface and destroy its passive state. As soon as the zinc dissolves completely or the conductor roll emerges from the rinsing solution, the conductor roll surface wants to become passive, resulting in a high corrosion rate during this passive film formation. The frequent removal, regrinding and eventual replacement of conductor rolls or roll sleeves casued by the high corrosion rate results in high maintenance costs and frequent shut downs of the electroplating process.